In one case, Pruetz and Bertolani, from the Leverhulme Centre for Human
Evolutionary Studies in Cambridge, UK, witnessed a chimpanzee extract a
bushbaby with a spear.

In most cases, the Fongoli chimpanzees carried out four or more steps to manufacture spears for hunting.

In all but one of the cases, chimps broke off a living
branch to make their tool. They would then trim the side branches and
leaves.

In a number of cases, chimps also trimmed the ends of
the branch and stripped it of bark. Some chimps also sharpened the tip
of the tool with their teeth.

Female lead

Adult males have long been regarded as the hunters in chimp groups.

But the authors of the paper in Current Biology said
females, particularly adolescent females, and young chimps in general
were seen exhibiting this behaviour more frequently than adult males.

"It's classic in primates that when there is a new
innovation, particularly in terms of tool use, the younger generations
pick it up very quickly. The last ones to pick up are adults, mainly
the males," said Dr Pruetz, who led the National Geographic
Society-funded project.

This is because young chimps pick the skill up from their mothers, with whom they spend a lot of their time.

"It's a niche that males seem to ignore," Dr Pruetz told BBC News.

Many areas where chimpanzees live are also home to the
red colobus monkey, which the chimps hunt. However, the Senegal site is
lacking in this species, so chimps may have needed to adopt a new
hunting strategy to catch a different prey - bushbaby.

The authors conclude that their findings support a
theory that females may have played a similarly important role in the
evolution of tool technology among early humans.